10" x 18" or 18" x 10" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 12.5" X 20.5"] w32h32 + Product Details Size -

+ Product Details Size - 28"w X 28"h is the size for the duct opening measurement only

+ Product Details Perfect Fit & Easy Sizing - Designed for a 16" x 32" OR 32" X 16" duct opening (measured at the opening)

+ Product Details Size – 18"w X 36"h is the size for the duct opening measurement only

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+ Product Details Size – 18" x 26" or 26" x 18" is the size for the duct opening measurement only

10" x 18" or 18" x 10" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 12.5" X 20.5"] w32h32 + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 10" x 18" or 18" x 10" duct opening (measured at the opening), with actual outer dimensions of 12. 5" W x 20. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 9. 75" x 17. 75" x 1" Premium Airflow Efficiency High performance cube core eggcrate design allows 95% airflow efficiency, reducing energy costs and maximizing HVAC system lifespan. Durable, Rust Free Aluminum